To address widespread concerns about cancer risks from residential magnetic field exposures, investigators from NCI and from the Children's Cancer Group have conducted a case-control study of childhood acute lymphoblastic leukemia. There was little evidence that living in houses characterized by high measured time-weighted average (TWA) magnetic field levels or by the highest wire-code category (a surrogate measure of the distance and characteristics of power lines near homes) increases the risk of acute lymphoblastic leukemia in children. Recent analyses focused on how well measurement data collected during a single visit made at an arbitrary hour of the day, day of week, and season estimate longer term residential 60-Hz magnetic field levels. We found a small but statistically significant seasonal effect, with residential magnetic field levels lower than the long term estimate (defined as the geometric mean of all 24 hour measurements from six bimonthly visits) in the Spring and about 4% greater during the Summer. No effect was found for the day of the week. However, we did find a systematic and appreciable diurnal effect, suggesting that an evening spot measurement may overestimate the long term estimate by 20% or more. To evaluate further the statistical associations between leukemia risk in children and their personal use of TV sets, hair dryers, and stereo headsets, and prenatal use by their mothers of sewing machines, extremely (ELF) and very low frequency (VLF) magnetic fields produced by a sample of each type of appliance were characterized in a measurement study of electrical appliances as used by volunteer children conducted in Washington, D.C. and its Maryland suburbs. ELF magnetic fields measured 10 cm from nozzles of hair dryers were elevated over the ambient by a mean factor of 17, whereas fields near headsets being used to listen to music were not distinguishable from ambient levels at 60-Hz. House sewing machines produced ELF magnetic fields that were elevated by a factor of 28 over ambient levels at the front surfaces of the lower abdomen of mothers. Estimated mean daily use of hair dryers, stereo headsets, and sewing machines were 2.6, 19, and 17 minutes, respectively. These data and previously published measurements of TV sets do not provide a consistent picture of increased (or decreased) leukemia risk in relation to increasing peak or TWA ELF magnetic field exposure. Overall, the results provide little evidence supporting the hypothesis that peak or TWA ELF magnetic fields produced by appliances are causally related to the risk of childhood leukemia. The etiology of brain tumors is poorly understood, and recorded incidence rates have increased dramatically over the past several decades. Whether this increase is, in part, real or is entirely an artifact of improved diagnosis is a controversial issue. Nonetheless, concern has arisen that one or more increasingly common environmental exposures might cause brain cancer. Examples include industrial chemicals, pesticides, food additives, and electromagnetic fields. In response to such concerns, and to advance understanding of environmental, behavioral and genetic causes of brain tumors, we are collaborating with investigators at three U.S. hospitals in conducting a case-control study of malignant and benign brain tumors. Factors under consideration include workplace exposures to chemical agents and electromagnetic fields, use of cellular telephones, dietary factors, family history of tumors, genetic determinants of susceptibility, home appliance use, reproductive history and hormonal exposures, viruses, medical and dental exposure to ionizing radiation, and other aspects of medical history. In our initial report, we found no association of cellular telephone use with brain tumors. Electrical appliances produce the highest intensity exposures to low-frequency electromagnetic fields. The relationship between appliance use and the risk of brain tumors is being explored in this hospital-based case-control study. The association of self-reported use of 14 common household appliances was investigated among the 678 cases and 686 controls who had completed self-administered questionnaires. Analyses of the data are underway. There was a significant association between glioma and history of any allergies (OR=0.67, 95% CI=0.52,0.86) or autoimmune diseases (OR=0.49,95% CI=0.35,0.69). Left-handedness also was found to be associated with a reduced risk of glioma (OR=0.7; 95% CI: 0.5-0.9). There was no association between self-reported history of polio vaccination and risk of brain tumors, an issue of concern in light of the contamination of early preparations of the Salk vaccine with SV40 virus, which has been shown to cause neural tumors in experimental animals. A positive association was seen between being currently married and the risk of meningioma and glioma, possibly because spouses encourage their partners to seek care or influence the type of care received. Jewish religion was associated with a significantly increased risk of meningioma (OR=4.3; 95% CI: 2.0-9.0). Having ever worked as a butcher or meat cutter; electrician; general farmer or farm worker; computer programmer or analyst; designer or decorator; or inspector, checker, examiner, grader or tester was associated with increased risk of glioma. The glutathione S-transferase-pi (GSTP)-Ile105Val variant was associated with increased glioma incidence, and the cytochrome P450 CYP2E1-rsaI variant was positively associated with the incidence of both glioma and vestibular schwannoma, particularly in younger subjects. Both genes encode enzymes involved in the metabolism of solvents and other possible workplace exposures. A collaboration with extramural investigators revealed that individuals with neurofibromatosis (NF) type 1 remain at significantly increased risk for developing astrocytoma beyond the first decade of life, and that such tumors are not always ?benign? pilocytic astrocytomas, as had been believed previously. In response to concerns about cancer risk from non-ionizing radiation of microwave and radio frequencies, an earlier study of cancer mortality among Korean War Naval Service veterans exposed to microwave radiation was reactivated. Deaths from all diseases and all cancers were significantly below expectation overall, and for the 20,021 sailors with high radar exposure potential compared to the 20,560 sailors with lower radar exposure potential. There was no evidence of increased brain cancer in the entire cohort. Testicular cancer deaths also occurred less frequently than expected. Nonlymphocytic leukemia was significantly elevated among men in high-exposure occupations but in only one of the three high exposure occupations, namely electronic technicians in aviation squadrons (SMR=2.2, 95% CI=1.3,3.7). Radar exposure had little effect on mortality in this cohort of US Navy veterans.